1. Field of the Invention
The present invention relates to a radiation curable lacquer for coating substrates. The lacquer is particularly useful in applications where the cured coating must remain clear, colorless, adherent, and solvent-resistant even after being heated as high as 350.degree. C.
2. Description of the Prior Art
Although lacquer resins curable under ultraviolet light are well known in the prior art, none meet the requirements for razor blade lacquer coatings: clear, colorless, adherent, solvent-resistant coatings having good thermal stability under the sintering conditions experienced during razor blade manufacture. As described in U.S. Pat. No. 3,071,856 and 3,518,110, coating the cutting edge of a razor blade with polytetrafluoroethylene dramatically decreases the amount of effort required to cut hair during shaving. To sinter that blade edge coating, a razor blade must be heated to temperatures between 200.degree. and 430.degree. C. Since blade edge coatings are applied after blade body coatings, body coatings must be ble to withstand these elevated temperatures without undesirable side effects, such as lack of adhesion or discoloration. Prior art polymer systems may contain a plurality of ester or urethane groups which can be thermally unstable at sintering temperatures.
A typical radiation curable lacquer is disclosed in U.S. Pat. No. 3,749,592, which describes a lacquer film particularly suggested for use in the finishing of wooden furniture. The preferred resin system comprises the addition reaction product of a hydroxy-functional lacquer grade resin and an ethylenically unsaturated monoisocyanate. Typical hydroxy-functional lacquer grade resins are nitrocellulose and hydroxyethyl cellulose. Cellulose acetate butyrate is also stated to be useful.
Another similar composition is described in U.S. Pat. No. 3,808,114. That patent describes a radiation curable composition comprising a major amount of unsaturated hydroxy-containing ester type polyester, and an effective amount of a light sensitizer, and optionally a small amount of a copolymerizable monomer. The polyester is produced by reacting an organic polybasic acid with a polyglycidyl ester having one or more epoxy groups in the molecule, and an unsaturated monobasic acid, under heating, by using an esterification catalyst in the presence of a polymerization inhibitor.
Finally, U.S. Pat. No. 3,864,133, describes a photopolymerizable composition which comprises a combination of a compound containing an ethylenically-unsaturated double bond and a urethane linkage, with at least one radical or linkage selected from the group consisting of secondary amino radical, tertiary amino radical, or urea linkage, and a photopolymerization initiator.
While each of the above patents describes a composition which is curable by ultraviolet radiation, they are not useful in the present invention because of failing to meet one or more of the above requirements for razor blade body coatings.
Accordingly, a need exists for radiation curable razor blade coatings which can be cured rapidly at low temperatures, and which after curing will possess the desired properties of hardness, adhesion, solvent resistance and thermal stability necessary for use as a razor blade body coating.